This invention relates to a wheel supported wagon for transporting a granular material such as grain and of the general type disclosed in U.S. Pat. No. 5,615,990 issued to the assignee of the present invention. As shown in this patent, a wheel supported frame supports a gravity discharge hopper or container having sloping side walls extending to a bottom wall, and a rectangular discharge opening is formed within one of the side walls adjacent the bottom wall. A generally flat closure door or panel is supported for sliding movement by parallel spaced tracks mounted on the one side wall for movement between a lower position closing the discharge opening and a retracted open position allowing grain to flow from the chamber defined by the container. The grain may flow into an auger unit as disclosed in the above-mentioned patent or may flow onto an inclined chute from which the grain fal by gravity into a receiving conveyor. The closure door is moved from a lower position closing the discharge opening and an elevated or upper open position by a rack and pinion mechanism wherein the rack is connected to the door, and a hand wheel is connected to rotate the pinion, as described in the above-mentioned patent.
When grain is transported in the wagon, the grain settles and becomes compacted and results in producing substantial pressure against the closure door in its closed position. This requires that substantial torque, for example, up to 150 foot pounds, be applied to the pinion by the hand wheel in order to raise the door to its open position. In order to reduce the grain pressure against the door in its closed position and to reduce the torque required to open the door, it is known to mount a small metering door on the outside of the primary closure door by means of a set of closely spaced tracks secured to the closure door. The rack actuator is connected to the small metering door so that rotation of the hand wheel first opens the metering door to allow a small flow of grain from the container, thereby reducing the grain pressure on the primary closure door. Since the small opening within the primary closure door weakens the closure door, it has been found necessary to weld knobs or projections to the floor of the container and outboard of the bottom edge of the primary closure door or to weld a reinforcing bar to the bottom edge of the primary closure door across the metering opening to prevent outward bending of the primary closure door. The knobs or projections or reinforcing bar result in obstructing the free and smooth flow of grain through either the metering opening or under the primary closure door when the metering door or the closure door is in its open position.